This invention relates to a control unit for supplying power to a circuit, and in particular to such a control circuit for an automotive application.
In a modern automobile, relays are often used to obviate the need for high current capacity wiring being routed to control switches in the vehicle cabin, and also to obviate the need for such control switches to be rated to carry such high currents. An application of such is the use of a relay having its coil connected to the high beam circuit, and its high current contacts used to make a circuit to driving lights. Without the use of the relay, the extra current load of the driving lights, in addition to the high beam current load of the existing driving lights, would result in failure of the high/low beam switch and/or the headlight switch with normal vehicle wiring. While this could be obviated in vehicle manufacture by including heavier wiring and heavier rated switches, so that in the event a vehicle owner decided to install driving lights, the vehicle circuitry would be of a sufficient rating, this is generally not done, in order to save manufacturing costs.
For similar cost saving measures, such relays, which are usually electromechanical devices, although there is no reason why they could not be solid state (ie transistorised), have been utilised in other parts of the vehicle circuitry. This includes for switching the vehicle ignition circuitry and the vehicle fuel pump and fuel injection circuitry. In this manner, the more expensive high current capacity wiring can be run on as short a route as possible, in circuit with the vehicle fuse box, the relay contacts, and the ignition coil (or ignition coils) primary (which can carry at least 4 amps), and similarly in circuit with any fuel pumps and fuel injection pressurisation pumps. The relay coils, which require perhaps 5% or less current to actuate than the load drawn by the circuits that the contacts actuate, can utilise much lighter wiring connected to the vehicle ignition switch, and a much lower current rating on the contacts in the vehicle ignition switch than would be the case if the circuits were connected to the ignition switch directly.
A very obvious application of such an arrangement is in the solenoid assembly which is used to actuate the vehicle starter motor. However in the case of the starter motor, the solenoid is only operated when the vehicle ignition is turned to the “start” position.
In the case of relays which connect to the ignition and any fuel pump circuitry, these must be actuated when the ignition is set to both the “run” and “start” positions.
Modern vehicle immobilisers, which can be stand-alone or incorporated into alarm systems, are usually wired into the circuitry in a vehicle to interrupt power to the vehicle ignition or fuel pump(s), unless over-ridden by a person who has the key to the alarm. In the past, keys were literally just that, although in more modern alarms electronic keys have been proposed, from simple resistive networks, and numeric keypads, to complex encryption techniques involving binary code strings and code hopping arrangements. In all of these arrangements, the immobiliser must be wired into the vehicle circuitry. This involves modifying existing vehicle circuitry in order to fit the immobiliser, which is time consuming and requires some knowledge of the vehicle circuitry on the part of the installer, or investigation to determine the nature of the vehicle circuitry when the installer is not familiar with it.
It is an object of this invention to provide an immobiliser system which overcomes some of the above problems, or at least provides an alternative to known immobiliser systems.
Throughout the specification, unless the context requires otherwise, the word “comprise” or variations such as “comprises” or “comprising”, will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.